Extra Dimensional Signatures at CLIC

Many models predict the existence of additional spatial dimensions that lead to new and distinct phenomenological signatures for future colliders which have center of mass energies in the TeV range and above. Most of the models in the literature fall into one of the three following classes: (i) the large extra dimensions scenario of Arkani-Hamed, Dvali and Dimopoulos(ADD)[1]. This model predicts the emission and exchange of large Kaluza-Klein(KK) towers of gravitons that are finely-spaced in mass. The emitted gravitons appear as missing energy while the KK tower exchange leads to contact interaction-like dimension-8 operators. (ii) A second possibility are models where the extra dimensions are of TeV scale in size. In these scenarios there are KK excitations of the SM gauge (and possibly other SM) fields with masses of order a TeV which can appear as resonances at colliders. (iii) A last class of models are those with warped extra dimensions, such as the Randall-Sundrum Model(RS)[3], which predict graviton resonances with both weak scale masses and couplings to matter. High energy lepton colliders in the multi-TeV range with sufficient luminosity, such as CLIC, will be able to both directly and indirectly search for and/or make detailed studies of models in all three classes. The case of direct searches is rather straightforward as we are producing the new physics, such as a KK resonance, directly. Indirect searches are more subtle but the capability of making high precision measurements at lepton colliders allows us to probe mass scales far in excess of the collider center of mass energy, in some cases by more than an order of magnitude. For most models of type (i) or (iii) which deal with the hierarchy problem, if no signal is observed by the time the mass scales probed by CLIC are reached, the motivation behind these particular models will be greatly weakened if not entirely removed. In what follows, for simplicity, we will only focus on searches involving the process e+e− → f f̄ . From studies performed for both NLC/TESLA and LEP we know that this channel provides an excellent probe of the parameter spaces of extra-dimensional models and we expect that this will continue to be true at even higher energies.